Active magnetic shim coils, used to correct field
inhomogeneities caused by susceptibility differences between tissue
interfaces, are typically composed of sets of cylindrical layers, with each
layer producing a magnetic field profile of a particular spherical harmonic.
A radically different approach to shimming is to dynamically and adaptively
control the flow of current over a given surface. This could be achieved with
the use of a network of metal-oxide-semiconductor field-effect transistors
(MOSFETs). In this work, we present computer simulations demonstrating the
benefits that a supplementary, region specific shim coil utilizing this
approach can provide, and experimental results of a proof-of-principle
prototype.